Method for producing metal-organic frameworks

ABSTRACT

The present invention relates to a method for the preparation of a metal-organic framework structure compound, the metal-organic framework structure compound being prepared such as well as the use of the metal-organic framework structure compound being prepared such as adsorbent.

The present invention relates to a method for the preparation of ametal-organic framework structure compound, the metal-organic frameworkstructure compound being prepared such as well as the use of themetal-organic framework structure compound being prepared such asadsorbent.

Heat of adsorption reservoirs provide the possibility of a nearlylossless storage of heat, particularly in the temperature range of up to250° C., over long periods of time. In particular in connection with thesolar thermal heating of buildings in regions of the earth with highseasonal fluctuations of the solarization, i.e. in all regions far awayfrom the equator, a need for such long-term heat reservoirs exists.Here, during the course of the year the highest amount of solar heatfrom thermal collectors is provided in summer, whereas however the needfor thermal heat predominantly exists in winter. In the sense of thedevelopment of a sustainable energy supply which is more focused ontoregenerative sources of energy the seasonal storage of heat for theheating of buildings is desirable and is a prerequisite for achievinghigh solar proportions in the solar thermal heating of buildings.

Also for many other applications the storage of heat in the temperaturerange of up to ca. 250° C. is an important subject. So e.g. in the caseof the decentralized power generation in plants with power-heat coupling(CHP) typically the problem of different temporal need profiles forpower and heat arises. For being capable of operating these plants in apower load optimized manner and for being capable of using the generatedheat, this heat has to be stored for a certain time, until it is needed.For that, heat reservoirs with high energy density and high efficiency,i.e. low heat losses, are required.

Till today, despite decades of research efforts, heat of adsorptionreservoirs have not become accepted on the market. Up to now, primarily,there has been a lack of adsorption materials which provide a large loadand heat turnover in the desired temperature range. The zeolites whichhave often been investigated and used for heat reservoir applications,e.g. zeolites with the structure types LTA and FAU, in particular thecommercially available zeolites A, X and Y, typically require for thedesorption a driving temperature difference of at least 100° C. betweenthe adsorber and the condenser, thus in the case of a condensertemperature of 35° C. a desorption temperature of at least 135° C. Withtypical flat plate collectors this temperature cannot be achieved or canonly be achieved with very low collector efficiency. Therefore, moreexpensive evacuated tube collectors or radiation-concentratingcollectors are required. With the mentioned zeolites under typical loadand unload conditions of a seasonal solar storage system, such as e.g.described in Mittelbach et al., “Solid sorption thermal energy storagefor solar heating Systems” (TERRASTOCK 2000, Stuttgart, Aug. 28-Sep. 1,2000), load turnovers of not higher than 0.18 gram water per gramzeolite are achieved. Thus, based on the density of a bed of thezeolite, reservoir energy densities of up to about 150 kWh/m³ can beachieved (A. Hauer, thesis, TU Berlin 2002, “Beurteilung festerAdsorbentien in offenen Sorptionssystemen für energetischeAnwendungen”).

With silica gels comparable energy densities are achieved, but here themain problem is the low usable temperature difference in the case ofunloading the reservoir.

Therefore, for the seasonal solar heat storage adsorbents are sought thewater adsorption properties of which are between those of typicalzeolites and typical silica gels. In particular materials are sought theadsorption isobars of which in the case of a water vapor pressure ofabout 56 hPa (corresponding to a water reservoir with a temperature of35° C.) in the temperature range of about 60-110° C. show a load changeof at least 0.2 g/g.

Metal-organic frameworks (MOFs) have been developed with respect to apossible use as high temperature hydrogen reservoirs or generally forthe sorptive storage of gas (U. Müller, “Metal-organicframeworks-prospective industrial applications”, J. Mater. Chem. 16(2006), p. 626-636). Due to the high porosity and surface area they aresuitable for diverse further fields of application which aretraditionally covered by zeolites, such as for example the heterogeneouscatalysis or for gas purification.

MOFs are characterized by a modular design. They consist of inorganicpolynuclear complexes (cluster) which serve as connectors in thenetwork. Here, the coordination number and the topology of the connectorare determined by the coordinating ligands being directed outwardly. Asconnecting members (linkers) bi-, tri- and multifunctional ligands areused.

With respect to the technical use, due to the good availability andnon-toxicity of the metal, in particularly MOFs on the basis of aluminumas metal clusters hold a lot of promise. However, for a lot ofapplications the low stability with respect to water and particularlywater vapor is a problem.

For example in the case of the storage of methane in an industrial scaleresidual moisture cannot be prevented. Also for the use in heat pumpsand refrigerating machines on the basis of the adsorption ofrefrigerants such as for example water, but also alcohols or naturalrefrigerants (propane, etc.) a stability with respect to water vapor isa prerequisite.

While in the case of the use of water as a refrigerant the stabilitywith respect to water directly arises as a result, also in the case ofother refrigerants the stability with respect to water is important,since for example in some process steps the contact with water vapor(atmospheric moisture during the preparation) cannot be avoided. Here,for example the MOF CAU-10-H seems to be very promising, because itexhibits high stability and at the same time good adsorptioncharacteristics.

For the synthesis of MOFs there are different possibilities; most MOFscan be synthesized by solvothermal syntheses. In this case a metal saltand an organic compound are suspended in a solvent or solvent mixtureand the reaction mixture is heated in a pressure reactor. This is alsothe common synthesis for CAU-10-H which can be found in literature (H.Reinsch, M. A. van der Veen, B. Gil, B. Marszalek, T. Verbiest, D. deVos and N. Stock, Chemistry of Materials, 2013, 25, 17-26): As areaction mixture a suspension of isophthalic acid (1,3-H₂BDC) andAl₂(SO₄)₃*18H₂O in DMF and water (1:4 parts) is used. The synthesis isconducted in an autoclave with Teflon liners for 12 h at 135° C. It isreported that during the synthesis in a glass reactor an unknown,crystalline minor phase was obtained. In this literature the synthesisof CAU-10-H was conducted in a 37 ml autoclave. It is mentioned that ascale-up in larger autoclaves is conceivable, but no evidence for thatis provided.

Especially water-stable MOFs which should be used as sorption materialfor heat transformation applications are prepared with water at excesspressure which results in the known, technical large-scale problems:

-   -   1. Due to the typical reaction temperatures (>100° C.) it is        necessary to work under excess pressure and in corresponding        vessels (autoclaves).    -   2. This complicates the reaction control (no view into the        vessels) and increases the costs enormously, particularly in the        case, when solvothermal syntheses should be used.    -   3. The use of glass flasks is hardly possible or only in a        limited extent.

For MIL-160, a MOF which is isostructural to CAU-10-H, a synthesiswithout the use of pressure in aqueous solution is known in which furandicarboxylic acid is reacted with aluminum(III) chloride over a periodof time of 24 hours. The purification is achieved by means ofcentrifugation. On the one hand, the use of aluminum(III) chloride whichis corrosive and not water-stable is a disadvantage. The purification bymeans of centrifugation is time-consuming and effortful with respect tothe required equipment.

DE 10 2014 215 568 A1 discloses a method for the preparation of anadsorbent out of metal-organic framework structures. In this case itseems to be possible to prepare the structures at atmospheric pressure.A solvent mixture of DMSO and water is used, wherein a relatively lowamount of water and a relatively high amount of DMSO (at least 50% byweight) are used. The target is to achieve with the DMSO a boiling pointof higher than 100° C. The water in the reaction mixture only has aminor role, and DMSO is assumed to be decisive for the success of theinvention. DMSO has the disadvantage that it forms explosive mixtureswith some metal salts which are also used in the synthesis of the MOF.The reaction times are in the order of 24 hours and thus, in comparisonto the present invention, are extremely long. The document does notdisclose the use of an aqueous solution for the synthesis.

US 2011/0282071 A1 discloses photo-active triazole structures. Anexample for an aromatic dicarboxylic acid is given. But the synthesis ofthe aromatic dicarboxylic acid in aqueous solution is not disclosed.

DE 10 2006 043 648 A1 teaches a method for the preparation of MOFs asadsorbent. The synthesis is conducted in an organic solvent having acomparatively high boiling point, e.g. in DMF. The reaction time is inthe order of 5 days.

DE 10 2005 039 654 A1 relates to mesoporous MOF compounds. It isdescribed to be decisive that in every case the structural features ofat least one nitrogen atom in the heteroaromatic of the linker and of atleast three substituents X in the form of carboxyl groups (or their thioderivatives) have to be fulfilled. Otherwise the large specific surfaceareas and the desired mesoporous structure would not be achieved. Thus,it recommended against the use of aromatic dicarboxylic acids. Thesynthesis is conducted in organic solvent.

The use of water is not recommended. With 4 days the reaction times arevery long. Desirable would be a method for the preparation of MOFs which

-   -   in comparison to the methods of prior art requires less reaction        time,    -   is harmless with respect to the environment,    -   does not impose special requirements on the working safety (e.g.        danger of explosion),    -   does not require a considerable amount of equipment (e.g.        autoclave) and    -   makes MOFs available in very good quality, particularly with        high water stability and large specific surface area.

Therefore, it was an object of the present invention to provide asynthesis route for CAU-10-H and structurally related MOFs whichovercomes the disadvantages of prior art.

In a first aspect, this object is solved by a method for the preparationof a metal-organic framework structure compound in which at least onemetal salt comprising a metal cation which is selected from the groupconsisting of the transition metals, Mg, and Al as well as combinationsthereof is reacted with a linker compound, characterized in that thereaction is conducted in an aqueous solution at a pressure of 1.5 bar orless. Here, the linker compound is selected from the group consisting ofsubstituted and unsubstituted aromatic dicarboxylic acids and aromaticdicarboxylates as well as combinations and mixtures thereof.

An “aromatic dicarboxylic acid” or an “aromatic dicarboxylate” is acompound which comprises at least one aromatic ring, particularlyexactly one aromatic ring, as a structural element which is substitutedwith at least two, particularly exactly two, carboxyl groups. Thearomatic may comprise a five-ring aromatic of the following group:thiophene, pyrrole, furan, imidazole, pyrazole, oxazole and isoxazole,thiazole; or a six-ring aromatic of the group consisting of phenyl,pyridine, pyrazine, pyrimidine and pyridazine.

According to the present invention, aromatic dicarboxylic acids arepreferably structures of the general formula 1. According to the presentinvention, aromatic dicarboxylates are preferably structures of thegeneral formula 2, wherein the phenyl group may be replaced by anotheraromatic or heteroaromatic ring, in particular a five-ring aromatic ofthe following group: thiophene, pyrrole, furan, imidazole, pyrazole,oxazole and isoxazole, thiazole; or a six-ring aromatic of the groupconsisting of pyridine, pyrazine, pyrimidine and pyridazine. Inpreferable embodiments the phenyl ring is not replaced by other groupsso that the linker compound is preferably isophthalic acid, anisophthalate or a derivate thereof. In alternative embodiments thelinker compound is selected from trimesic acid, thiophene dicarboxylicacid, pyridine dicarboxylic acid and furan dicarboxylic acid as well astheir carboxylates and derivatives. As shown here, the carboxyl groupsmay be arranged in the positions 1 and 3. But also the positions 1 and 2and the positions 1 and 4 are according to the present invention.

Preferably, the groups R1 to R4 are independently from each otherselected from hydrogen, carboxyl, hydroxyl, nitro, amino, methyl, etherand halogenide groups as well as combinations thereof. In preferableembodiments all groups R1 to R4 are hydrogen. In preferable embodimentsR3 is selected from amino, nitro, hydroxyl, methyl ether and methylgroup.

In preferable embodiments the linker compound is selected fromisophthalic acid and isophthalates. According to the present invention,the terms “isophthalic acid” and “isophthalates” also comprise theirderivatives, in particular derivatives comprising a substitution at theposition 2, 4, 5 or 6. As suitable substituents hydroxyl, nitro, amino,methyl, ether and halogenide groups as well as combinations thereof canbe mentioned.

Preferably, the reaction is conducted in aqueous solution. Since manyaromatic dicarboxylic acids are occasionally characterized by poorsolubility in water, it is preferable to use the aromaticdicarboxylates. Preferably, the dicarboxylates are used in the form oftheir salts, preferably as sodium, potassium, or ammonium salts.

Preferred metals are Fe, Co, Ni, Zn, Zr, Cu, Cr, Mo, Mg, Mn, Al, Pd andcombinations thereof, wherein particularly preferred are Al, Fe, Cu, Cr,Zr as well as combinations thereof.

In also preferred embodiments the metals are selected from Sc, Ti, V,Cr, Mn, Fe, Co, Ni, Cu, Zn as well as combinations thereof. Inparticularly preferred embodiments the metal is selected from Al and Fe.Especially in the case of the use of aluminum it is possible to prepareextremely water-stable framework structure compounds. Preferably, themetals are used in the form of their water-soluble salts, particularlythe sulfates, nitrates, carbonates, chloride oxides or halogenides. Butalso other salts each can be used.

According to the present invention, “reacting in aqueous solution”preferably means that substantially no organic solvents are used in thereaction medium. Advantageous aqueous solutions comprise less than 10%by volume, in particular less than 5% by volume, further preferably lessthan 2% by volume and particularly preferably less than 1% by volume oforganic solvent such as DMF. In preferable embodiments the reactionmedium does not at all contain any organic solvent. The proportion ofwater in the aqueous solution is in particular higher than 50% byvolume, more preferably at least 70% by volume, particularly higher than80% by volume and particularly preferably at least 90% by volume or atleast 99% by volume.

In special embodiments short-chain alcohols having carbon chain lengthsof 1 to 4 carbon atoms, in particular ethanol, can be used in thereaction media of this invention. Their proportion is preferably limitedto at most 20% by volume, more preferably at most 10% by volume of thesolvent used.

The main issue of the present invention is a new synthesis approach inwhich, different from prior art, a substantially pressure-less synthesisis conducted. As a further aspect, the present invention preferablycomprises the use of solutions of the educts and not of solids and/orsuspensions. In particular in combination with the pressure-lesssynthesis, this is an advantage. So, as solvent preferably water can beused, and a pressure reactor is not required.

Therefore, in a preferable design of the method according to the presentinvention the reaction is conducted at a pressure of at least 900 mbar,particularly at least 1 bar. In preferable embodiments the pressure isat most 1.2 bar or at most 1.1 bar. Thus, the reaction can be conductedat atmospheric pressure. From that direct economic advantages follow,when the preparation method is translated into an industrial scale. Forexample, a continuous production can be realized by removing productbeing prepared from the process. This can be achieved by filtration. Anadvantageous design of the method according to the present Inventioncomprises the isolation of the metal-organic framework structurecompound being prepared by means of filtration. Isolation of the productby means of filtration can be realized in a continuous method in aneasier manner than the isolation by means of centrifugation.

Furthermore, the working-up is substantially easier, since only one stepof washing is necessary and no thermal activation for removing, forexample, residues of DMF.

As a result, with that the recyclability is significantly increased, andthe residues of the synthesis batch can directly be introduced into theclarification plant without any further post-treatment. Thus, also theproduct is directly free of organic solvent.

In a preferable design of the method according to the present inventionthe reaction is conducted at a temperature of 80 to 120° C.,particularly 90 to 110° C. In one embodiment the reaction temperature isat most 100° C. The reaction is in particular conducted at the boilingpoint of the reaction medium.

A further technical advantage of the synthesis methodology according tothe present invention is that, compared with the poor solubility of thearomatic dicarboxylic acid (e.g. isophthalic acid), the aromaticdicarboxylate (e.g. isophthalate) can easily be dissolved in water. Inparticular, when it should be translated into an industrial scale, thisresults in advantages, since the reaction time is considerably reduced,from 12 h, such as in literature, to, for example, 6 h or 3 h in aflask. As a consequence thereof a higher STY (space-time yield) can beachieved. Therefore, in a preferable design of the method according tothe present invention the reaction is conducted over a period of time of10 hours or less, in particular of 8 hours or less, particularlypreferably 6 hours or less.

In a further preferable design of the method according to the presentinvention the reaction is conducted under irradiation of the aqueoussolution with microwaves. But also other methods for heating thereaction vessel which are common for a person skilled in the art areaccording to the present invention.

In contrast to the synthesis which is known from literature, accordingto preferred methods according to the present invention the startingmaterials are aromatic dicarboxylates (e.g. isophthalates) and not thearomatic dicarboxylic acid (e.g. isophthalic acid) which ischaracterized by poor solubility in water. Therefore, in the synthesiswhich is known from literature due to the poor solubility it isnecessary to use DMF as a solvent and an increased temperature.

For the method according to the present invention each arbitraryaromatic dicarboxylate can be used (e.g. isophthalate). Preferably usedare sodium dicarboxylates (e.g. sodium isophthalates), potassiumdicarboxylates (e.g. potassium isophthalates), ammonium dicarboxylates(e.g. ammonium isophthalates) and mixtures thereof.

In principle, for the method according to the present invention, allmetal salts being described above can be used. Preferably used are ironand aluminum salts.

In contrast to the synthesis which is known from literature preferablyaluminum sulfate in combination with sodium dicarboxylate (e.g. sodiumisophthalate) as well as at the same time an inorganic base,particularly sodium hydroxide, calcium hydroxide, potassium hydroxide,ammonia or sodium aluminate in a solution and in a glass vessel insteadof a Teflon vessel are used.

In the first instance, the use of Al sulfate is not obvious, since theformation of minor phases, in particular alunite (KAl₃[(OH)₆(SO₄)₂]), isconsiderably increased. For avoiding or for minimizing the formation ofthese minor phases, preferably potassium hydroxide, sodium hydroxide,calcium hydroxide, ammonia or sodium aluminate is added as a base. Here,sodium aluminate is used as combined metal source and base which is nottaught in literature. Accordingly, in a preferable design of the methodaccording to the present invention as metal salt aluminum sulfate isused. In a further preferable design of the method according to thepresent invention a base is added to the aqueous solution. Preferably,the base is selected from the group consisting of ammonia, sodiumhydroxide, potassium hydroxide, sodium aluminate and potassiumaluminate. Particularly preferable is sodium aluminate.

In an alternative preferable design of the method according to thepresent invention as metal salt iron(III) chloride is used.

Subject matter of the present invention is also a metal-organicframework structure compound which is prepared or can be prepared by themethod according to the present invention being described here. Thesecompounds are characterized by a particularly high resistance againstwater. Preferably, the metal-organic framework structure compound has aspecific surface area according to BET of 500 m²/g or more.

In addition, subject matter of the present invention is the use of themetal-organic framework structure compound as an adsorbent, wherein theadsorbed material (adsorbate) is preferably water, ethanol, methane,CO₂, H₂ or a mixture thereof. According to the present invention isparticularly the use of the metal-organic framework structure compoundsbeing described herein for applications such as gas storage, catalysis,dehumidification and heat transformation (e.g. heat pumps, refrigeratingmachines).

With the method according to the present invention high yields of morethan 90%, based on the linker compound, can be achieved. Themetal-organic framework structure compounds being prepared with thismethod have the same or larger surfaces areas, the same or highercapacities with respect to gas sorption and thus the same or bettertechnical properties than metal-organic framework structure compoundsbeing prepared according to a prior art method. In addition, themetal-organic framework structure compounds which have been prepared byreaction in aqueous solution are characterized by the absence ofresidues of organic solvents.

The present invention will be explained in greater detail by means ofthe following examples.

EXAMPLES

For the samples to be investigated at the beginning of the ageingprocess being independent on cycles a starting measurement with nitrogen(N₂) at 77 kelvins was conducted on a NOVA 3000e of the companyQuantachrome. Via the nitrogen measurement at 77 kelvins informationabout the change of the pore structure (distribution of the pore radii),pore volumes as well as about the internal surface area (BET) can begathered. For removing humidity and foreign gases from the samples,before the actual measurement, they were baked out in high vacuum for 24h at 120° C. Subsequently, the dry weight of the sample was measured bymeans of an analytical balance of the company Sartorius with the classof accuracy I. Subsequently, complete isotherms in adsorption anddesorption were measured and evaluated. The relative pressure range wasbetween p/p0=0.05-0.999 in the case of adsorption and p/p0=0.999-0.1 inthe case of desorption. The pore volume was calculated according to thedensity functional theory (DFT) and according to the model of Dubininand Astakhov (DA). The internal surface area was calculated according tothe model of BrunauerEmmett-Teller (BET) between p/p0=0.05 and 0.15.

Comparative Example

Synthesis:

200 mg of 1,3-isophthalic acid (1,3-H₂BDC, 1.20 mmol), dissolved in 1 mLof N,N-dimethyl formamide (DMF), were mixed with 800 mg ofAl₂(SO₄)₃*18H₂O, dissolved in 4 mL of H₂O, and treated in a Teflon-linedsteel autoclave for 12 hours at 135° C.

Working-Up:

After allowing to cool down to room temperature the product wasfiltrated and washed with water in an ultrasonic bath. The white solidobtained was dried and subsequently activated at 120° C. in vacuum for24 hours.

The specific surface area of the product was S_(BET)=525 m²/g and thepore volume was 0.27 cm³/g.

Embodiment Example 1

Synthesis:

A solution of 0.75 mol (125 g) of isophthalic acid in 600 ml of DMF and2400 ml of water and 0.72 mmol (483 g) of Al₂(SO₄)₃*18H₂O were heated ina 5000 ml three-necked flask to 135° C.

In a 5 L flask 483 g (0.72 mol) of Al₂(SO₄)₃*18H₂O were completelydissolved in 2.4 L of water. To the aluminum sulfate solution 125 g(0.75 mol) of isophthalic acid, dissolved in 600 mL of DMF, were addedin portions.

The solution was refluxed under stirring for a period of time of 48 h.

Working-Up:

The solid formed was filtered off with the help of a fluted filter (5-13μm), resuspended in H₂O and placed in an ultrasonic bath for 30 minutes.This procedure was repeated three times. Subsequently, the white solidwas dried for 5 days at 90° C. in the drying oven and for 1 day at 120°C. in the vacuum oven.

After the purification 156.8 g of a white solid with S_(B)ET=578 m²/gwere obtained. The single crystalline phase was identified by means ofX-ray powder diffraction analysis as CAU-10-H. FIG. 6 shows the powderdiffractogram of CAU-10-H.

Embodiment Example 2

Synthesis:

5 L of a 0.5 M sodium isophthalate solution were prepared by making upsodium hydroxide (199.99 g; 5 mol) and isophthalic acid (415.33 g; 2.5mol) in a graduated volumetric flask with H₂O to a volume of 5000 ml.Furthermore, 2 L of a 0.5 M aluminum sulfate*18H₂O solution (666.15 g; 1mol) and 2 L of a 0.5 M sodium aluminate solution (81.79 g; 1 mol), eachby making up in a graduated volumetric flask with H₂O to a volume of2000 mL, were prepared each. For the reaction 2.16 L of sodiumisophthalate solution (0.5 M) and 180 mL of ethanol were combined andunder stirring 810 mL of aluminum sulfate solution (0.5 M) and 540 mL ofsodium aluminate solution (0.5 M) were added. Subsequently, the reactionwas conducted for 6 h under reflux and stirring.

Working-Up:

The solid obtained was filtered off, washed with a plenty of water andethanol and dried over night at 90° C. 207 g (92% yield) of a whitepowdery solid (S_(BET)=580 m²/g) were obtained, and this was identifiedas CAU-10-H by means of X-ray powder diffraction analysis. The N₂sorption isotherm is shown in FIG. 1; filled squares describe theadsorption curve and empty squares describe the desorption curve.

Embodiment Example 3

Synthesis:

For the synthesis 100 mL of a 0.5 M sodium isophthalate solution wereprepared by making up sodium hydroxide (3.99 g, 0.1 mol) and isophthalicacid (8.30 g; 0.05 mol) in a graduated volumetric flask with H₂O to avolume of 100 ml. Furthermore, 100 mL of a 0.5 M aluminum sulfate*18H₂Osolution (33.308 g; 0.05 mol) and 100 mL of a 2 M sodium hydroxidesolution (7.99 g; 0.2 mol), each by making up in a graduated volumetricflask with H₂O to a volume of 100 mL, were prepared each. For thereaction 127.5 mL of H₂O, 7.5 mL of ethanol and 90 mL of sodiumisophthalate solution were combined and under stirring 45 mL of aluminumsulfate solution and 22.5 mL of sodium hydroxide solution were added.Subsequently, the reaction was conducted for 6 h under reflux andstirring.

Working-Up: The solid obtained was filtered off, washed with a plenty ofwater and ethanol and dried over night at 100° C. A powdery solid(S_(BET)=573 m²/g) was obtained which was identified by means of X-raypowder diffraction analysis as CAU-10-H. Furthermore, the reactionproduct contained a minor phase (sodium alunite, NaAl₃(OH)₆(SO₄)₂;#(ICSD)=44626). The N₂ sorption isotherm is shown in FIG. 2; filledsquares describe the adsorption curve and empty squares describe thedesorption curve.

Embodiment Example 4

Synthesis:

5.25 mL of a 0.5 M sodium isophthalate solution was stirred up with 4.5mL of water. Under stirring 5.25 mL of a 0.5 M FeCl₃ solution wereadded. Subsequently, the reaction was conducted for 6 h at 95° C. in themicrowave under stirring.

Working-Up:

The solid obtained was filtered off, washed with a plenty of water andethanol and dried over night at 90° C. It was possible to identify it asFe-MIL-59. FIG. 3 shows the water sorption isotherm obtained with thissubstance.

Embodiment Example 5

For a further synthesis of Fe-MIL-59 100 mL of m-Na₂-BDC solution (0.5M) and 50 mL of water were combined and under stirring 100 mL of FeCl₃solution (0.5 M) were added. The reaction was conducted under vigorousstirring and reflux for 6 hours. The solid obtained was filtered off bymeans of a very fine filter and the solid was washed thoroughly withwater. The product was dried in the drying oven (90° C.) for 3 days. Anorange-brown solid was obtained. The yield was 12.55 g (max. 12.8 g,98%). The powder diffractogram measured is shown in FIG. 4. As acomparison the diffractogram of vanadium MIL-59 which is isostructuralis shown.

Embodiment Example 6

7.5 mL of Na₂TDC solution (0.5 M) were provided, and under stirring5.625 mL of AlCl₃ solution (0.5 M) and 1.875 mL of NaAlO₂ solution (0.5M) were added. The reaction was conducted for 3 h at 95° C. understirring in the microwave. The solid obtained was filtrated and washedwith water and ethanol. An analysis resulted in a surface area (BET) of1024 m²/g and a pore volume=0.4381 cm³/g. FIG. 5 shows the N₂ sorptionisotherm.

A synopsis of the comparative example and the embodiment example 1results in the finding that the synthesis method according to thepresent invention in comparison to common methods which are conducted inthe presence of an increased pressure results in metal-organic frameworkstructure compounds with larger specific surface area.

From the comparison of embodiment example 1 and the embodiment examples2 and 3 it is obvious that the use of isophthalates in aqueous reactionmedia substantially reduces the reaction time.

Embodiment example 4 shows that the reaction does not only work withaluminum as the metal component.

Embodiment example 6 shows that the reaction can analogously beconducted with other aromatic dicarboxylic acids.

What is claimed is:
 1. A method for the preparation of a metal-organicframework structure compound comprising the steps of: reacting at leastone metal salt comprising a metal cation which is selected from thegroup consisting of the transition metals and Al as well as combinationsthereof, with a linker compound, wherein the reaction is conducted at apressure of less than 1.5 bar in aqueous solution, and wherein thelinker compound is an isophthalate or a derivate thereof.
 2. The methodaccording to claim 1, wherein the aqueous solution comprises less than10% by volume of organic solvents.
 3. The method according to claim 1,wherein the reaction is conducted at a temperature of 80 to 120° C. orhigher.
 4. The method according to claim 1, wherein the reaction isconducted over a period of time of 10 hours or less.
 5. The methodaccording to claim 1, wherein the linker compounds are structures of thegeneral formula 2:

wherein the groups R1 to R4 are independently from each other selectedfrom hydrogen, hydroxyl, nitro, amino, methyl, ether and halogenidegroups as well as combinations thereof.
 6. (canceled)
 7. The methodaccording to claim 1, wherein the metal salt is selected from the groupconsisting of iron and aluminum salts.
 8. (canceled)
 9. The methodaccording to claim 1, wherein to the aqueous solution a base is added.10-14. (canceled)
 15. The method according to claim 1, wherein thereaction is conducted at the boiling point of the reaction medium.